1. Field of the Invention
The present invention relates to control devices in transceivers and, more particularly, to a control device in a transceiver which is designed to suppress the unnecessary radiation of frequency signals resulting from control steps repeated at a constant period to thereby realize a good quality of communication.
2. Description of the Related Art
There is shown a general arrangement of a transceiver 1 in FIG. 8 in which a voice signal produced at a microphone 2 of the transceiver 1 is modulated at a transmitter 3 and then sent through an antenna duplexer 4 to an antenna 5 to be transmitted from the antenna to a partner transceiver 1' in the form of electromagnetic or radio waves.
On the other hand, the transceiver 1, when receiving radio waves transmitted from the transceiver 1' at the antenna 5, sends them through the antenna duplexer 4 to a receiver 6 where the radio waves are demodulated to an original voice signal that is then supplied to a receiver 7 such as loudspeaker or an ear receiver.
A control circuit 8 in the transceiver 1 acts to perform control for establishing a radio communication circuit between the transceivers 1 and 1'.
A synthesizer 9 is also provided in the transceiver 1 to generate a frequency signal that determines a radio channel frequency on the basis of the channel assignment of the control circuit 8.
The arrangement and operation of the transceiver 1' are exactly the same as those of the transceiver 1.
In the meantime, recent tendency of transceivers is that an increasing number of functions including, for example, multi-channel access and the like involve the complicated control of the radio communication circuit, with the result of a complicated control procedure.
In order to cope with such circumstances, a microprocessor (which will be referred to merely as MCU, hereinafter) has been incorporated in the control circuit 8. An example of the arrangement of such a control circuit is shown in FIG. 9.
The control circuit of FIG. 9 comprises an MCU 10 as a nucleus, an EPROM 11 for storing therein a control program, an IDROM 12 for storing therein individual identification codes for respective transceivers, a RAM 13 for temporarily storing therein information on control, a crystal resonator 14 for generating a reference clock frequency for the MCU 10, a detection circuit 15 for performing various detections including, for example, the detection of a power source voltage, the MCU 10 being connected to the EPROM 11, IDROM 12 and RAM 13, respectively, by means of data buses a, b and c.
These data buses a, b and c are operated at all times on an operational clock frequency f.sub.o of the MCU 10.
The control operation of the control circuit 8 having such an arrangement is shown, as an example, by a flowchart in FIG. 10.
More in detail, in the exemplary flowchart of FIG. 10, the control circuit 8 sequentially judges whether or not to cause such a speech ending means as a switch (not shown) to terminate the conversation in a speech mode (step 16), whether or not to provide a low-voltage indication on the basis of a detection signal received from the detection circuit 15 (step 17), and whether or not to terminate the conversation on the basis of a speech-end request signal transmitted from the partner transceiver 1' (step 18), and then executes, on the basis of the corresponding judgement result, such control as to transfer to the associated speech end flow or low-voltage indication flow.
At this time, if the conversation is normally maintained, then the control circuit 8 executes repetitively the processings from the step 16 to the step 18.
The control processing time for only one cycle from the step 16 through the step 17 to the step 18, which time is determined by the number of program steps, is constant.
That is, such control steps are executed at intervals of a constant period T, during which the control program data is repetitively read at the period T out of the EPROM 11 through, for example, the data bus a connected between the MCU 10 and the EPROM 11. This means that a series of pulses, which has the operational clock frequency f.sub.c and flows through the data bus a, is AM-modulated at a period of T (sec) or at a frequency of 1/T. Thus, in this case, frequency spectra satisfying the following relationship between the operational clock frequency f.sub.c and its harmonics nf.sub.c will inevitably take place: EQU nf.sub.c .+-.m/T
where m and n denote respectively an integer.
Such frequency spectra are illustrated in FIG. 11. As will be clear from the drawing, innumerable frequency spectra inevitably occur since the frequency 1/T is usually much smaller than the operational clock frequency f.sub.c (for example, f.sub.c =4 MHz and 1/T=10 kHz).
The generation of such innumerable frequency spectra enhances the possibility of generating the same frequency as the radio communication channel and for example when radio waves receiving at the transceiver 1 are weak, this disadvantageously causes the generation of beat noise, thus making conversation difficult with the partner transceiver.
Such a disadvantage during wave reception of the transceiver will occur even during transmissive operation of the transceiver. That is, even in the transmission mode of the transceiver, such countless frequency spectra as mentioned above take place and act to increase the unnecessary radiation, with the result that the deterioration of communication quality cannot be avoided.
In this way, the prior art transceiver control circuit has had such a problem that, when the control circuit repetitively executes the control steps necessary for transmitting and receiving operations, this causes the generation of innumerable frequency spectra, which results in that the unnecessary radiation of noise such as typical beat noise during the wave reception takes place with the deteriorated communication quality.
In view of such circumstances, it is an object of the present invention to provide a control circuit in a transceiver which can reduce unnecessary noise radiation during transmitting and receiving operations to minimize the generation of beat noise and realize a good quality of communication.